Up to 24 people are still missing following the eruption, which caught hikers on Mount Ontake by surprise.
Most of the bodies were found at the ash-covered summit where many of them were resting or having lunch.
All but one of the dead recovered so far was hit by rocks flying at speeds of up to 190mph, according to doctors. The other victim died from inhaling hot air.
"The bulk of the rocks are estimated to be between the size of a human fist and a head," Takayuki Kaneko, a volcanologist at the University of Tokyo's Earthquake Research Institute, said.
"They fell so densely that some broke up (after hitting other rocks and objects) and scattered," he told public broadcaster NHK.
By Ruchi Singh
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